Field of the Invention
This invention relates to a method for control of a drive for a tool or workpiece, especially for producing or machining an optical lens, in which pilot control takes place depending on a frequency of movement which corresponds to a reference variable and to a device with a control apparatus for controlling of a drive, especially for a tool or workpiece, especially preferably for machining of an optical lens, having a pilot control apparatus for pilot control of the drive depending on a frequency of movement which corresponds to a reference variable.
Description of Related Art
Fast and efficient machining of a workpiece with a tool requires a correspondingly fast and exact tool movement. In industrial fabrication, generally so-called “computerized numerical controls” (CNC) are generally used for exact positioning of tools, there being controls of the corresponding drives.
Promptly reaching a target position is a prerequisite for fast and efficient machining. Rates of change of the setpoint which result herefrom however can lead to a so-called contouring error. The contouring error is a characteristic for a control deviation, for a ramp-shaped characteristic of the setpoint a steady-state value for the contouring error being set. The contouring error can be reduced by a control with high gain or speed gain being used, but the risk of the occurrence of instabilities being increased.
In particular, in methods which are encompassed under the expression “high speed cutting”, hereinafter also called HSC, very high rates of change of the reference variable or a value which corresponds to it, especially the position setpoint, very high feed rates, very high cutting or machining rates and/or very high accelerations are used. To reduce the contouring error, the use of pilot control is known which roughly pilots a manipulated variable which is to be controlled, therefore, for example, the current of a drive, from a reference variable, therefore especially a position setpoint so that the control need compensate for only comparatively small differences. The use of this pilot control can lead to reduction of the contouring error.
German Patent Application DE 196 37 632 A1 relates to a method for controlling a feed unit of a machine tool, for compensation of the effects of friction and a contouring error which has been induced thereby a pilot value being determined. The latter is added to the control for pilot control of a manipulated variable. A controller cascade is used, the setpoints supplied to this cascade being used for determining the pilot value.
German Patent Application DE 10 2006 006 162 A1 relates to a controller structure for position control, a pilot current for a drive being determined from a position setpoint. This pilot current is differentiated and multiplied by a factor. This factor is designed to make it possible to adapt the pilot control to different applications.
European Patent Application EP 1 439 437 A1 and corresponding U.S. Pat. No. 7,031,799 B2 relate to a method for active damping of low frequency oscillations on numerically controlled machine tools. At a multiplication site, the difference of the derived rpm and the set rpm is multiplied by a factor; this is intended to allow continuous control of the active damping of the low frequency oscillations. However, it is not disclosed how this gain could be determined.
European Patent Application EP 1 560 325 A1 and corresponding to U.S. Pat. No. 7,224,141 B2 relate to a device for monitoring a motor position, a feed lowpass filter being used with a transfer function for elimination of ripples by quantization errors. In particular, a derived position instruction can be amplified and filtered by the lowpass filter for elimination of ripple. With respect to the gain, it is disclosed that it can be between 40 and 50%, but also in the vicinity of 100%. However, it is questionable whether, and optionally how, this factor could be determined.